Delay-Lines with attributes of low insertion loss, low cost, high power signal handling, and which are variable are desired for numerous microwave applications. Especially, in modern high frequency radar and communication systems, the antenna pattern must be moved at very rapid rates and this is normally achieved in phase-array antennas through the use of a matrix of small radiator elements whose radiation phases are systematically and electronically varied. The necessary phase gradients across the antenna are usually generated in discrete steps by a plurality of such electronic phase shifter elements. This application system requires phase shifter which has low insertion loss, variable, and can deal with high signal.
State-of-art delay lines are based on active device technologies such as Field-Effect Transistor (FET) and P-I-N diode; however, these are not capable of providing all the desired attributes mentioned earlier because the transistor fabrication process (MMIC) is costly and requires high resolution.
Currently, it is possible to make a passive delay line using a transmission-line structure and conventional dielectrics. This passive delay line can be made tunable using switches. The primary drawbacks concerning this type of delay line are: the insertion loss is dominated by the dielectric materials and a longer delay time further increases the insertion loss. Insertion loss can be minimized if a low loss tangent dielectric material is used. However, under current technologies the cost of the low loss tangent dielectrics is sufficiently high to limit their usage to high-end systems.
Prior art disclosed in U.S. Pat. No. 5,495,211, the capability of delay line for steering the beam in RF system uses the reconfigurable transmission line in which plurality of excitation beam/sources are used to change the conductivity to reconfigure the transmission line property. Using of the excitation beams would require the additional power to function the delay line requiring desired signal delay would not disadvantages for the RF systems.
In U.S. Pat. No. 4,603,310, the disclosed low insertion loss phase shifter (delay line) which uses a pair of diodes, connected back to back between the input and output of the circuit. A parallel resonant circuit made from an inductor in parallel with a capacitor and combination are series with a diode, is arranged at the common junction between the back to back diodes. As this structure is made of diodes and not suitable for dealing with the high input of signal,
Therefore, it is highly desirable to have delay lines that are passive and can offer characteristics such as: (i) low insertion loss, (ii) compact in size, and (iii) low cost. Additionally, it is desirable to have delay lines which have high signal handling capability and are tunable, yet cost-effective and friendly for manufacturing.
The present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below with reference to preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.